Cutting a solid surface to make a overlapping junction
You could use a Boolean Modifier. Though, the success of this method may depend on the topology of your mesh. It does not always give clean or desired results, but it may be worth a try.

Also you will want Solidify to be above Boolean in your modifier stack. And if you apply these modifiers, apply the Solidify first, and then apply the Boolean.

EDIT:
You could make something like this, where the selected mesh is the (already applied) Boolean target object.

If you put the selected orange edge, shown on the left, (one is extruded inward, and one extruded outward) in in the middle of the solidified wall thickness, and then preform the boolean operation, you will end up with submarine parts that will fit into each other as shown on the right.